Expandable and collapsible brain cannula

ABSTRACT

A method of accessing a target site within the brain of a patient, through the skull of the patient, with an expandable cannula.

The application is a continuation of U.S. application Ser. No.15/701,278, filed Sep. 11, 2017, which claims priority to U.S.Provisional Application 62/385,918, filed Sep. 9, 2016.

FIELD OF THE INVENTIONS

The inventions described below relate to the field of minimally invasivebrain surgery.

BACKGROUND OF THE INVENTIONS

Stroke is a common cause of death and disabling neurologic disorder.Approximately 700,000 patients suffer from stroke in the United Statesevery year. Hemorrhagic stroke accounts for 20% of the annual strokepopulation. Hemorrhagic stroke is due to a rupture of a blood vessel inthe brain, causing bleeding into the brain tissue and resulting in ahematoma (a blood mass) in the brain. Prompt removal of the blood massis necessary to limit or prevent long-term brain injury. Removal of theblood mass requires access through the skull and brain tissue, and thisis usually accomplished by inserting a cannula through a small burr holein the skull (created by a drill), or a larger hole created with a saw(a craniotomy or craniotomy hole), and forcing the cannula through thebrain. To minimize trauma to the brain, this is currently accomplishedwith a cannula and obturator assembly, in a method that entails pushinga fairly large cannula, with an obturator disposed in the lumen of thecannula and protruding distally from the cannula, into the brain, usingthe tip of the obturator to push aside brain tissue to minimize trauma.

Wilson, Apparatus and Methods for Performing Brain Surgery,WO2006/050047 (Nov. 5, 2006) proposed inserting a small diameterexpandable sleeve over a stylet, followed by forcing a larger diametercannula down into the sleeve. Translation of the rigid cannula down intothe sleeve serves to gradually expand the sleeve, from the proximal end(nearest the entry point) to the distal end (nearest the target site)and gently retract the brain. Also, Wilson discloses inserting a tubecomprising expandable braid covered in an expandable sleeve, in a smalldiameter configuration, and pushing on both the proximal and distal endsof the braid to force it expand and foreshorten, to create a large lumentube in the brain.

SUMMARY

The devices and methods described below provide for easier access tosurgical sites in the brain. The device comprises an expandable andcollapsible brain cannula which can be inserted into the brain in asmall diameter configuration compacted within a constraining tube,inserted to a desired depth near a target site such as a blood mass, andreleased from the tube to allow it to expand to a large diameterconfiguration and thereby provide a cannula large enough to permitpassage of the distal end of tools such as aspirators, macerators,ablation devices, stimulation electrodes, drug delivery devices ordrains and the like through the cannula and into the surgical site. Thecannula comprises a tube, braid or coil of resilient material, which isflexible enough to be compacted into a small diameter configuration tofit into an insertion tube, and resilient enough to expand within thebrain, gently expanding against surrounding brain tissue, to a largediameter configuration upon release from the insertion tube. The devicemay be made of pseudoelastic nitinol, shape memory nitinol, stainlesssteel, spring steel, and resilient polymers (including biodegradablepolymers), etc. The tube may be covered with an elastic sheath, toprevent intrusion of brain tissue into any gaps between filaments of abraid, turns of a coil, or gaps in a laser cut tube. In use, the cannulais compressed into a small diameter tube, and pushed through braintissue (preferably through the sulcus between folds or gyrus of thebrain), and the small diameter tube is withdrawn over the cannula toallow the cannula to expand. To remove the cannula, a small diametertube may be gradually slipped over the cannula, as the cannula is heldsteady to avoid sliding against brain tissue, until the entire cannulais compressed within the tube, whereupon the tube and compacted cannulaare removed from the brain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a patient with an intracerebral hematoma, and anexpandable cannula in place to provide access to the hematoma.

FIG. 2 illustrates a cannula system, with a cannula which is expandableand compressible, to expand from a small diameter configuration to alarge diameter configuration, and also compress from a large diameterconfiguration to a small diameter configuration.

FIG. 3 illustrates the cannula system of FIG. 2, modified with theaddition of an obturator.

FIG. 4 illustrates initial placement of the cannula system.

FIG. 5 illustrates pull-back of the delivery tube of the cannula systemto release the expandable cannula.

FIG. 6 illustrates removal of an obturator, after expansion of thecannula.

FIG. 7 illustrates a configuration of the cannula, after removal of thesheath.

FIG. 8 illustrates the use of a surgical tool through the expandedcannula.

FIG. 9 illustrates an initial step in the recapture of the cannula andits compression into the delivery tube.

FIG. 10 illustrates the configuration of the cannula system after thedelivery tube has been slipped over the entirety of the cannula andcompressed the cannula into its small diameter configuration.

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 illustrates a patient 1 with a blood mass 2 in the brain 3 thatnecessitates surgical intervention. An expandable cannula system 4 hasbeen inserted into the brain, with the distal end of the cannulaproximate the blood mass. The cannula system includes an expandablecannula 5 surrounded by an insertion tube 6, which, as described below,functions to constrain the cannula in a small diameter configuration. Asdepicted in FIG. 1, the cannula is in its small diameter configuration,and constrained by the insertion tube.

FIG. 2 illustrates a cannula system, with the cannula 5 which isexpandable and compressible, to expand from a small diameterconfiguration to a large diameter configuration, and also compress froma large diameter configuration to a small diameter configuration. Thecannula 5 comprises a resiliently expandable tube, which may be asolid-walled tube, a tube with numerous apertures in its wall, a braidedtube, a coil of resilient material, or a series of spring loadedinter-digitated sectioning pieces which is flexible enough to becompacted into a small diameter configuration to fit into an insertiontube, and resilient enough to expand within the brain, gently expandingagainst surrounding brain tissue, to a large diameter configuration uponrelease from the insertion tube. As depicted in FIG. 2, the cannula isin its small diameter configuration, and constrained by the insertiontube. The unconstrained, large diameter configuration may be uniformthroughout the length of the cannula. The device may be made ofpseudoelastic nitinol (pseudoelastic at body temperature), shape memorynitinol, stainless steel, spring steel, resilient polymers (includingbiodegradable polymers), etc. Preferably, the tube comprises apseudoelastic nitinol tube, laser-cut to remove much of the wallmaterial. The tube may be covered with an elastic or hydrogel sheath, toprevent intrusion of brain tissue into any gaps between filaments of abraid, turns of a coil, or gaps in a laser cut tube.

The cannula is compressed within the insertion tube 6, which has a smallinner diameter to allow for easy insertion into the brain. The cannulamay include one or more posts or pushwires 7, disposed at the proximalend of the cannula and extending proximally from the cannula, for use inholding the cannula steady while the insertion tube is withdrawnproximally to allow the cannula to expand. The posts may be permanentlyfixed to the cannula, and may comprise a continuation of a braid of thecannula, or they may be releasably attachable to the cannula.Preferably, the length of the insertion tube is shorter than the lengthof the posts, so that the tube may be slipped over the posts, and theposts may be grasped by the surgeon to hold the cannula in place,preventing unwanted inward or outward motion of the cannula, while thesurgeon is pulling the insertion tube outwardly to release the cannula,or pushing the insertion tube inwardly to recapture the cannula. Thelength of the posts needs to be sufficient to extend from the proximalend of the insertion tube or extraction tube when a proximal portion ofthe cannula is disposed within the distal end of the insertion tube orextraction tube. A flange (or one or more tabs) 8 is disposed on theinsertion tube proximal end, for use in pulling the insertion tubeproximally to uncover the cannula. The insertion tube may be scoredalong its length, so that upon withdrawal it may be torn open, so thatthe post(s) 7 may be shorter than the insertion cannula.

For access to a typical hematoma in the brain, the cannula may be 2 to20 cm long, with an unrestrained diameter of about 6 to 60 mm, awall-thickness of about 0.1 to 1 mm, depending on the material chosen.Preferably, the cannula is fabricated to provide a hoop strength ofabout 3.5N when unconstrained, or total outward force of about 2 to 5N(0.4 to 1 lb.) and more preferably about 3 to 4 N, or an average outwardforce of about 5 N/mm2, or 725 psi). The insertion tube is preferablyabout 1 to 3 mm in outer diameter, and 1.5 to 2.5 mm in inner diameter,and the cannula is compressible to a small diameter configuration whichfits into the insertion cannula.

FIG. 3 illustrates the cannula system of FIG. 2, modified with theaddition of an obturator. The system of FIG. 3 includes all thecomponents of the system of FIG. 1, and also includes an obturator 9.The obturator comprises a rod segment 10 with a small diameter that fitswithin the cannula in its compressed, small diameter configuration, anda large diameter conical tip 11. The tip has a proximally facingshoulder, which abuts the distal end of the cannula when the cannula isin its compressed, small diameter configuration within the insertiontube. The proximally facing shoulder has an outer diameter slightlylarger (perhaps as large as the outer diameter of the insertion tube)than the inner diameter of the cannula in its compressed configuration,so that the cannula cannot translate distally (deeper into the brain)relative to obturator while in its compression configuration. Theobturator may have a small flange 12 or other structure at its proximalend to serve as a handle, and to serve as a mount for sensors operablefor registration with a neuro-navigation system.

In use, the cannula is compressed into a small diameter insertion tube,and pushed through brain tissue (preferably between gyrus of the brain,avoiding puncturing gray matter to the extent possible), and the smalldiameter tube is withdrawn over the cannula to allow the cannula toexpand. To remove the cannula, the small diameter tube may be graduallyadvanced over the cannula, as the cannula is held steady to avoidsliding against brain tissue, until the entire cannula compressed withthe tube, whereupon the tube and compacted cannula are removed from thebrain.

The procedure is illustrated in FIGS. 4 through 10.

FIG. 4 illustrates initial placement of the cannula system. As shown inFIG. 4, a surgeon has inserted the assembled cannula system, through aburr hole 13, into the brain, so that the distal end of the assembledcannula assembly is near a target site within the brain (the hematoma).

FIG. 5 illustrates the initial pull-back of the insertion tube of thecannula system to release the expandable cannula. As shown in FIG. 5,the surgeon has pulled the insertion tube proximally, while holding thecannula steady to avoid distal or proximal translation of the cannula(that is, movement along the longitudinal axis of the cannula) thatmight result in sliding the cannula over or through brain tissue. Thesurgeon may hold the cannula in place by grasping the post(s) 7. Whileholding the cannula steady, the surgeon pulls the insertion tubeproximally, by pulling on the tab(s) 8. As the insertion tube movesproximally, the cannula is gradually released from its constraint, andexpands gradually, from the distal end to the proximal end. If anobturator is used, as the cannula expands, the inner diameter of thecannula will grow to exceed the diameter of the obturator. The obturatorcan pulled proximally, so that the proximal face abuts a portion of thecannula still constrained by the insertion tube. Alternatively, thesurgeon may hold the obturator and cannula, at their proximal ends, soas to fix the obturator longitudinally relative to the cannula.

FIG. 6 illustrates removal of an obturator, after expansion of thecannula. In FIG. 6, the insertion tube has been completely removed andthe obturator has been removed from the lumen of the cannula. Thecannula is unconstrained by the insertion tube, and has expanded towardits unconstrained large diameter configuration. Expansion of the cannulamay be limited by the surrounding brain tissue, or the bone surroundingthe burr hole.

FIG. 7 illustrates a configuration of the cannula, after removal of thesheath. In this illustration, a small bore burr hole has been created inthe skull of the patent, and the expandable cannula has been insertedand the insertion tube removed to allow the cannula to expand. Theunconstrained diameter of the cannula in this illustration is largerthan the diameter B of the burr hole created by the surgeon, so that,upon expansion within the brain, the cannula expands toward itsunconstrained diameter, to achieve a large diameter configuration whichis larger diameter C than the burr hole, except where constrained by theskull surrounding the burr hole.

FIG. 8 illustrates the use of a surgical tool through the expandedcannula. With the cannula in a large diameter configuration, the surgeonmay insert the distal end of any suitable surgical device through thecannula and into the target site, such as the hematoma.

FIG. 9 illustrates an initial step in the recapture of the cannula andits compression into the delivery tube, to be performed after the bloodmass has been removed (or other intracranial procedure has beencompleted). As shown in FIG. 9, the surgeon slips an extraction tube 14over the post(s) 7 and the proximal end of the cannula, and graduallyforces the extraction tube distally over the cannula. The surgeon holdsthe posts, to prevent the cannula from translating distally (furtherinto the brain) due to the force applied by the extraction tube.Preferably, the surgeon also prevents the cannula from movingproximally, to avoid sliding the cannula outer wall over brain tissue.The extraction tube may be the very tube used as the insertion tube, ora new tube. If a new tube is used, it may have a larger diameter thanthe insertion tube, since it may not be necessary to compact the cannulato the same small diameter that facilitates insertion.

FIG. 10 illustrates the configuration of the cannula system after thedelivery tube has been slipped over the entirety of the cannula andcompressed the cannula into its small diameter configuration. At the endof this step, the cannula has been compressed along its entire length toa small diameter configuration and cannula system, including the cannulaand the tube, may be removed from the brain.

As depicted in the figures, the device facilitates a method of accessinga target site within the brain of a patient, through the skull of thepatient. The method, performed by a surgeon, entails providing theexpandable and collapsible cannula, characterized by a small diameterconfiguration and an unconstrained large diameter configuration, withthe cannula disposed in the small diameter insertion tube in its smalldiameter configuration, and inserting the cannula, while disposed in theinsertion tube, through an opening in the skull of the patient, andpushing the cannula distally through brain tissue until a distal end ofthe cannula is proximate the target site. To expand the cannula, thesurgeon pulls the insertion tube proximally while preventing the cannulafrom moving distally, to allow the cannula to resiliently expand towardits large diameter configuration, to the extent permitted by surroundingbrain tissue. With the cannula in place and opened to a large diameterconfiguration, the surgeon will insert the distal end of a surgicalinstrument through the cannula and into the target site. Afterperforming a surgical procedure, such as aspiration of a blood mass, thesurgeon can remove the cannula by compressing the proximal end of thecannula and advancing a tube having a diameter smaller than the cannulain its expanded configuration over the cannula, to compress the cannulatoward its small diameter configuration, and then pulling the cannulaproximally to withdraw the cannula from the brain.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Theelements of the various embodiments may be incorporated into each of theother species to obtain the benefits of those elements in combinationwith such other species, and the various beneficial features may beemployed in embodiments alone or in combination with each other. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

I claim:
 1. A cannula system for accessing a target site within a brainof a patient, said system comprising: a cannula comprising a resilientlyexpandable tube, said cannula having a distal end adapted for insertioninto the brain of the patient and a proximal end; an insertion tubehaving a first length and adapted for insertion into the brain of thepatient; wherein the cannula is compressible to a small diameterconfiguration to fit inside the insertion tube, and expandable to anunconstrained large diameter configuration; and an extraction tube thatfits over the cannula, the extraction tube having a diameter smallerthan the cannula in the unconstrained large diameter configuration. 2.The cannula system of claim 1, further comprising: an obturator having aproximal end, a distal end, and a rod segment with a diameter that fitswithin the cannula when the cannula is in the small diameterconfiguration.
 3. The cannula system of claim 2, wherein the obturatorfurther includes a conical tip at the distal end.
 4. The cannula systemof claim 2, wherein the obturator further includes a flange at theproximal end.
 5. The cannula system of claim 2, wherein the obturatorfurther comprises: a tip with a proximally facing shoulder which abutsthe distal end of the cannula when the cannula is in its compressed,small diameter configuration and within the insertion tube, saidproximally facing shoulder having an outer diameter larger than theinner diameter of the cannula when the cannula is in its compressed,small diameter configuration.
 6. The cannula system of claim 2, whereinthe obturator further comprises: a tip with a proximally facing shoulderwhich abuts the distal end of the cannula when the cannula is in itscompressed, small diameter configuration and within the insertion tube,said proximally facing shoulder having an outer diameter larger as largeas an outer diameter of the insertion tube.
 7. The cannula system ofclaim 1, wherein the resiliently expandable tube is selected from thegroup consisting of a solid-walled tube, a tube with a plurality ofapertures in its walls, a braided tube, a coil of material, and a seriesof spring loaded inter-digitated sectioning pieces.
 8. The cannulasystem of claim 1, wherein the cannula, in the large diameterconfiguration, further comprises a distal section having a firstdiameter, an intermediate section having a second diameter, and aproximal section having a third diameter, wherein the first diameter islarger than the second diameter.
 9. The cannula system of claim 8,wherein the third diameter is larger than the second diameter.
 10. Thecannula system of claim 1, wherein the cannula, in the large diameterconfiguration, further comprises a distal section having a firstdiameter, an intermediate section having a second diameter, and aproximal section having a third diameter, wherein the third diameter islarger than the second diameter.
 11. The cannula system of claim 1,further comprising: a post disposed at the proximal end of the cannulaand extending proximally from the cannula, wherein the post is shorterthan the insertion tube.
 12. The cannula system of claim 1, wherein thecannula comprises pseudoelastic nitinol, shape memory nitinol, stainlesssteel, spring steel, or resilient polymers.
 13. The cannula system ofclaim 1, wherein the cannula is covered with an elastic sheath.
 14. Thecannula system of claim 1, wherein the cannula is covered with ahydrogel sheath.
 15. The cannula system of claim 1, wherein theinsertion tube further comprises a flange disposed on the proximal endof the insertion tube.
 16. The cannula system of claim 1, wherein theinsertion tube is scored along its length, whereby the insertion tube isconfigured to be torn open along its length.
 17. The cannula system ofclaim 1, wherein the cannula has a diameter in the unconstrained largediameter configuration of 6 to 60 mm and provides a hoop strength of3.5N when in the unconstrained large diameter configuration.
 18. Thecannula system of claim 1, wherein the cannula has a diameter in theunconstrained large diameter configuration of 6 to 60 mm, a length of 2to 20 cm, and provides a total outward force of 2 to 5N or 3 to 4 N. 19.The cannula system of claim 1, wherein the cannula has a diameter in theunconstrained large diameter configuration of 6 to 60 mm and provides anaverage outward force of 5 N/mm2.
 20. The cannula system of claim 1,wherein the insertion tube comprises an insertion tube diameter and theextraction tube comprises an extraction tube diameter, wherein saidextraction tube diameter is larger than said insertion tube diameter.